1. Field of the Invention
The present invention relates to arc quenching for high voltage electrical devices and equipment wherein under certain conditions of operation a high voltage electrical arc is produced that must be quenched to eliminate an undesirable current flow. More particularly, the present invention relates to the use of a high temperature refractory coating on the arc extinguisher side walls of circuit breakers.
2. Description of the Prior Art
In general, circuit breakers having arc extinguishing apparatus for electrical contacts have been widely used to electrically interrupt power when overcurrent flows through power source lines. These circuit breakers typically have arc extinguishing apparatus such as described in U.S Pat. No. 4,866,226, incorporated by reference herein. These arc extinguishers typically comprise a plurality of stacked, substantially U-shaped arc extinguishing plates which surround the fixed and movable contacts of the circuit breaker. When the circuit breaker contacts are opened, creating an arc therebetween, the arc is driven and expanded in the direction of the extinguishing plates through electromagnetic action, causing the arc to divide into sections and be cooled down by the arc extinguishing plates so as to be extinguished.
The arc extinguishing plates are typically surrounded by a non-conducting single or double side wall consisting of fiber, such as cotton, or wood pulp, plastic, such as phenolic materials, or fiberglass. Holes are punched into these side walls to position and support the arc extinguisher plates, thereby creating the necessary spacing between the plates to enhance arc extinguishing capability. The protruding ends of the arc extinguisher plates are typically attached to the side wall by staking or spinning, the side wall and each pair of adjacent arc plates defining a chute for extinguishing the arc segmented by the plates.
Arc extinguisher side walls have in the past been formed of fibers within a melamine resin matrix, as disclosed in U.S. Pat. No. 4,950,852. Such resins are used to provide a continuous source of arc-quenching gaseous molecular compounds evolved by the heat of the arc.
Others have used side walls formed of a composite material of fiber and a net or porous material having more than 35% apparent porosity to make the arc extinguisher side walls light-absorbing. See U.S. Pat. No. 4,516,002.
U.S. Pat. No. 4,975,551 discloses an arc extinguishing composition comprising an arc-interrupting compound, such as melamine, which is disposed along the path of the arc in combination with a binder composition.
U.S. Pat. No. 4,251,699 discloses an arc-quenching composition comprising a dicyandiamide and an elastomeric binder. The composition is placed sufficiently near the arc such that the heat of the arc causes deionizing and extinguishing gas to be emitted from the composition, thereby extinguishing the arc. The same effect is achieved as disclosed in U.S. Pat. No. 4,444,671 with a composition comprising hexamethylenetetramine, either alone or in combination with a binder or impregnated on other material.
Others have sprayed resin coatings onto the side walls or applied high temperature adhesive tape to the side wall.
Despite these attempts, none of the known devices or techniques fully satisfies all the needs of a reliable circuit breaker arc extinguisher, especially at higher voltages, such as 600 volts.
The fiber material used in the side walls frequently experiences arc resistance surface penetration, and thermal breakdown. Many prior art arc extinguisher devices experience voltage tracking up the side walls as a result of carbon buildup on the side walls from the intense heat of the arc. Gaps in the areas where arc plates intersect the side wall provide a path for voltage to escape the arc extinguisher, rendering it less effective. This problem has persisted in the art for about thirty years.
Accordingly, it is an object of the invention to provide a composition for rendering arc extinguisher side walls resistive to thermal shock.
It is another object of the invention to provide a coating for sealing all gaps between arc plates and side walls to prevent voltage from escaping the arc extinguisher.
It is yet another object of the invention to prevent voltage tracking up the arc extinguisher side walls by eliminating carbon buildup on the side walls.
It is another object of the invention to improve the arc resistance surface penetration on fiber materials comprising the side walls.
It is still another object of the invention to prevent thermal breakdown of the side walls.
It is another object of the invention to provide additional mechanical support to the side wall of the arc extinguisher.
These and other objects are achieved by the preferred embodiments of the invention, as will now be discussed.